diff --git a/jedi/plugins/stdlib.py b/jedi/plugins/stdlib.py
index 7a07494d..57e2c1e0 100644
--- a/jedi/plugins/stdlib.py
+++ b/jedi/plugins/stdlib.py
@@ -708,14 +708,18 @@ def _os_path_join(args_set, callback):
     if len(args_set) == 1:
         string = u''
         sequence, = args_set
+        is_first = True
         for lazy_context in sequence.py__iter__():
             string_contexts = lazy_context.infer()
             if len(string_contexts) != 1:
                 break
             s = get_str_or_none(next(iter(string_contexts)))
-            if string is None:
+            if s is None:
                 break
-            string += os.path.sep + force_unicode(s)
+            if not is_first:
+                string += os.path.sep
+            string += force_unicode(s)
+            is_first = False
         else:
             return ContextSet([compiled.create_simple_object(sequence.evaluator, string)])
     return callback()
diff --git a/test/test_api/test_completion.py b/test/test_api/test_completion.py
index a9dc66e1..2e52240b 100644
--- a/test/test_api/test_completion.py
+++ b/test/test_api/test_completion.py
@@ -210,6 +210,9 @@ os_path = 'from os.path import *\n'
         (f2, os_path + 'dirname(__file__) + "%stest_ca' % s, None, ['che.py']),
         (f2, os_path + 'dirname(abspath(__file__)) + sep + "test_ca', None, ['che.py']),
         (f2, os_path + 'join(dirname(__file__), "completion") + sep + "basi', None, ['c.py']),
+        (f2, os_path + 'join("test", "completion") + sep + "basi', None, ['c.py']),
+
+        # inside join
         (f2, os_path + 'join(dirname(__file__), "completion", "basi', None, ['c.py"']),
         (f2, os_path + 'join(dirname(__file__), "completion", "basi)', 43, ['c.py"']),
         (f2, os_path + 'join(dirname(__file__), "completion", "basi")', 43, ['c.py"']),